Slide connectors with frictional locking means

ABSTRACT

This invention relates to slide connectors which connect a plurality of boards in Ell, Tee, and Cross, connections. The connection is made by the retaining slide rails affixed to the edges of the boards that has a cross section having a narrowed-down root, each of which slidably engages one of four retaining slide grooves included in four sides of a connecting bar wherein the retaining slide groove has a cross section matched to the cross section of the retaining slide rail, which includes a narrowed-down opening. The connecting bar includes at least one hole of a finite depth having a noncircular cross section disposed at at least one extremity thereof, or a through hole of a noncircular cross section disposed therethrough in a coaxial relationship with respect to the geometric center line of the cross section of the connecting bar. A threaded cylindrical locking member having an outside diameter slightly greater than the inside diameter engages the noncircular hole included in the connecting bar nd creates a small amount of distortion on the cross sectional geometry of the connecting bar, which results in a frictional locking between the connecting bar and the retaining slide rails. When the threaded cylindrical locking member is removed, the cross sectional geometry of the connecting bar returns to the original shape and the slidable engagement between the connecting bar and the retaining slide rails is restored.

BACKGROUND OF THE INVENTION

This patent application is a Continuation-In-Part application to patentapplication Ser. No. 653,898 entitled "Skewed Double Groove Slide Joint"filed on Sept. 24, 1984.

In recent years, there has been a strong demand for office furniture andhome furniture which can be assembled, disassembled and reassembled bythe users. As a consequence, a new family of furniture known as"Knock-Down" or "K-D" system furniture has made a sizable inroad intotoday's furniture market. In order to compete with permanently assembledconventional furniture in the upper class furniture market, the "K-D"furniture must meet a few requirements: Firstly, they must comprisecomponents of compact sizes and light weights: Secondly, thesecomponents must be assembled into an assembly having a high degree ofrigidity and strength. Thirdly, the assembly must have an attractiveappearance that displays the perfection and quality displayed by highquality conventional furniture. Fourthly, they must provide aflexibility in design and assembly whereby the users can build thecustom designed furniture by using mass produced components. Without anyexception, all "K-D" type furnitures available in the present day marketfail to satisfy the aforementioned requirements. The key to the perfect"K-D" type furnitures is the perfect connecting system that enables theassembly of component boards into an assembly having a high degree ofrigidity and strength, precise and accurate joints, and an extremelyattractive appearance, wherein high quality is maintained after repeatedassembly and disassembly of the furniture. The connecting system musthave such a universality that the users are able to construct theircustom-designed furniture by using mass-produced components, in whichsense, the furniture system should be an "I Design and Assemble" or"IDA" system rather than a simple "Knock-Down" or "K-D" system.

The primary object of the present invention is to provide a connectorsystem for "I Design and Assemble" or "IDA" furniture systems.

Another object is to provide a connector system for connecting aplurality of boards in Ell, Tee, and Cross connections with a highdegree of dimensional precision and a high level of structural rgidityand strength.

A further object is to provide a connector system that is assembled anddisassembled in a sliding relationship and locked by frictional meanswherein repeated assembly and disassembly does not leave any marks onthe connector system and does not alter the physical state thereof.

Yet another object is to provide a connector system that can bemass-produced by using todays metal-working or plastic-formingtechnology, i.e., extrusion method.

Yet a further object is to provide a connector system including a foursided connector bar including four retaining slide grooves respectivelydisposed in four sides; and plurality of retaining slide railsrespectively affixed to the edges of a plurality of boards and athreaded cylindrical locking member interferingly engaging a noncircularhole disposed axially through the connector bar.

These and other objects of the present invention will become clear asthe description thereof proceeds.

BRIEF DESCRIPTION OF FIGURES

The present invention may be described with a greater clarity andspecificity by referring to the following figures:

FIG. 1 illustrates a front end view of a board including a retainingslide rail affixed to one extremity thereof.

FIG. 2 illustrates a front end view of a connector bar that connects theboards shown in FIG. 1 in ell, tee or cross connections.

FIG. 3 illustrates a cross section of the connector bar of FIG. 2 takenalong a plane 3--3 as shown in FIG. 2.

FIG. 4 illustrates an end view of a countersunk head locking screw.

FIG. 5 illustrates a side view of the countersunk head locking screwshown in FIG. 4.

FIG. 6 illustrates a front end view of three boards connected in atee-connection comprising the elements shown in FIGS. 1, 2 and 5.

FIG. 7 illustrates a cross section of a filler bar that slidably engagesthe unused retaining slide groove included in the connector bar of FIG.2.

FIG. 8 illustrates a front ends view of another board including aretaining slide rail affixed to one extremity thereof.

FIG. 9 illustrates a front end view of a connector bar that connects theboards shown in FIG. 8 in ell, tee or cross connections.

FIG. 10 illustrates an end view of a locking member.

FIG. 11 illustrates a cross section of the locking member of FIG. 10taken along a plane 11--11 as shown in FIG. 10.

FIG. 12 illustrates a front end view of three boards connected in atee-connection comprising the elements shown in FIGS. 8, 9 and 11.

FIG. 13 illustrates an end view of another locking member usable inconjunction with the connector bar shown in FIG. 2 or 9.

FIG. 14 illustrates a side view of the locking member shown in FIG. 13.

FIG. 15 illustrates the other end view opposite to one end view shown inFIG. 13 of the locking member.

FIG. 16 illustrates a front end view of a further board including aretaining slide rail affixed to one extremity thereof.

FIG. 17 illustrates a front end view of a connector bar that connectsthe boards shown in FIG. 17 in ell, tee, and cross connections.

FIG. 18 illustrates a cross section of the connector bar of FIG. 17taken along a plane 18--18 as shown in FIG. 17.

FIG. 19 illustrates a front end view of two boards connected in anell-connection comprising the elements shown in FIGS. 16, 17 and 5.

FIG. 20 illustrates a cross section of a filler bar that slidablyengages the unused retaining slide grooves included in the connector barof FIG. 17.

FIG. 21 illustrates a front end view of a another board including aretaining slide rail affixed to one extremity thereof.

FIG. 22 illustrates a front end view of a connector bar that connectsthe boards shown in FIG. 21 in ell, tee, or cross connections.

DESCRIPTION OF PREFERRED EMBODIMENTS

In FIG. 1 there is illustrated a front end view of a board 1 including aretaining slide rail 2 affixed to one extremity 3 thereof. The retainingslide rail 2 comprises a pair of skewed rails 4 and 5 of substantiallyconstant width and finite height which extend from the web 6 of achannel 7 in two diverging oblique directions, respectively. The flangesof the channel 7 include a pair of tongues disposed at the extremitiesthereof. The channel 7 is affixed to the extremity of the board by meansof a tongue and groove joint wherein glueing or bonding may be furtheremployed to strengthen the joint therebetween.

In FIG. 2 there is shown an end view of a connector bar 8 which is afour-sided elongated member. Four retaining slide grooves 9, 10, 11, and12 having a cross section matched to the cross section of the retainingslide rail 2 shown in FIG. 1 are disposed in four sides of the connectorbar 8, respectively. Each of the retaining slide grooves includes a pairof skewed grooves 13 and 14 of substantially constant width and finitedepth which extend from the side surface of the connector bar 8 in twodiverging oblique directions, respectively. The connector bar 8 includesa noncircular hole 15 of square cross section disposed in asubstantially coaxial relationship with respect to the geometric centerline of the cross section of the connector bar 8. The noncircular hole15 is disposed in such a way that the core portion of the cross sectionof the connector bar 8 is substantially of a thin walled hollow squaretubing. At least one extremity of the noncircular hole 15 includes acountersunk 16. It should be understood that the noncircular hole 15 mayhave a finite depth instead of being a through hole as shown in FIG. 2.

In FIG. 3 there is shown a cross section of the connector bar 8 takenalong a plane 3--3 as shown in FIG. 2 wherein the noncircular hole 15having at least one countersink 16 disposed at at least one extremitythereof is further illustrated.

In FIG. 4 there is shown an end view of a locking screw 17 having a flatcountersunk head with a hex socket 19.

In FIG. 5 there is shown the full length of the the locking screw 17including the flat countersunk head 18 and a shank 20 with threads 21formed over a partial or total length of the shank 20. The shankdiameter as well as the maximum diameter of the threaded portion thereofis slightly greater than the minimum inside dimension of the squarecross section of the noncircular hole 15 included in the connector bar8. When the locking screw 17 engages the noncircular hole 15 in aself-threading action, the interference between the outside diameter ofthe shank 20 of the locking screw 17 and the inside surface of thenoncircular hole 15 deforms the flat sides of the noncircular hole 15into a slightly oval shaped geometry that provides frictional lockingbetween the retaining slide rail 2 and the retaining slide groove 9which prevents the sliding movement there-between. The deformation ofthe cross section of the connector bar 8 created by the locking screwtakes place within the elastic limit of the material of the connectorbar and, consequently, when the locking screw is removed from thenoncircular hole 15, the sliding movement between the retaining sliderail 2 and the retaining slide groove 9 is restored. The countersink 16included in the noncircular hole 15 of the connector bar 8 is matched tothe countersunk head 18 of the locking screw 17 whereby the flat end ofthe countersunk head 18 of the locking screw 17 becomes flush with theend surface of the connector bar 8 when the locking screw 17 is fullythreaded into the noncircular hole 15 of the connector bar.

In FIG. 6 there is shown a front end view of three boards 22, 23 and 24respectively including retaining slide rails 25, 26 and 27 connected toeach other in a tee-connection by means of the connector bar 28including four retaining slide grooves 29, 30, 31 and 32. The unusedgroove 32 is filled up by a filler bar 33 slidably engaging theretaining slide groove 32. The locking screw 34 engaging and expandingthe noncircular hole centrally disposed through the connector bar 28frictionally locks the retaining slide rails 25, 26, and 27 in theretaining slide grooves 29, 30 and 31, respectively. Of course, thelocking screw 34 also frictionally locks the filler bar 33 in theretaining slide groove 32. The flat countersunk head of the lockingscrew 34 is large enough to substantially fill up the noncircular holeincluded in the connector bar 28, which combination provides anattractive appearance for the tee-connection of the boards.

In FIG. 7 there is shown a cross section of the filler bar 33 that fillsup the unused retaining slide groove included in the connector bar flushto its side surface. The filler bar 33 has a cross section same as theretaining slide rail 2 shown in FIG. 1 minus the base channel 7.

In FIG. 8 there is shown a front end view of a board 35 including aretaining slide rail 36 comprising a pair of skewed rails 37 and 38having essentially the same construction as the pair of skewed rails 4and 5 shown in FIG. 1 with one exception being that the skewed rails 37and 38 have reparate roots while the skewed rails 4 and 5 have a commonroot.

In FIG. 9 there is shown a front end view of a connector bar 39including four retaining slide grooves 40, 41, 42 and 43 disposed infour sides of the connector bar 39, respectively. Each of the retainingslide grooves 40, 41, 42 and 43 includes a pair of skewed groovesessentially the same as those included in the connector bar 8 shown inFIG. 2 with one exception being that the pair of skewed grooves includedin the retaining slide grooves 40, 41, 42 and 43 have separate openingswhile the pair of skewed grooves included in the retaining slide groovesof the connector bar 8 have a common opening. The connector bar 39includes a noncircular hole 44 coaxially disposed lengthwise through theconnector bar 39. The square cross section of the noncircular hole 44 isdisposed in such a way that the central portion of the cross section ofthe connector bar 39 is substantially of a thin walled square tubing.

In FIG. 10 there is illustrated an end view of a locking screw 45including a flat countersunk head 46 with a hex socket 47 and a squarewasher 48.

In FIG. 11 there is illustrated a cross section of the locking screw 45taken along a plane 11--11 as shown in FIG. 10. The locking screw 45 hasan enlarged extremity 49 opposite to the flat countersunk head 46, whichenlarged extremity 49 is partially or fully threaded. The outsidediameter of the enlarged portion 49 of the shank of the locking screw 45is slightly greater than the minimum inside dimension of the squarecross section of the noncircular hole 44 of the connector bar 39 and,consequently, when the locking screw 45 threadedly engages thenoncircular hole 44, the cross section of the connector bar 39experiences a small amount of deformation which frictionally locks upthe sliding movement between the retaining slide rail 36 and theretaining slide grooves 40, etc. The size of the square washer 48retained in position intermediate the flat countersunk head 46 and theenlarged portion 49 of the locking screw 45 is made to fit into and fillup the noncircular hole 44 included in the connector bar 39. It shouldbe mentioned that the locking screw 45 may be used in conjunction withthe connector bar 8 shown in FIG. 2 minus the countersink 16.

In FIG. 12 there is illustrated a front end view of three boards 50, 51and 52 including the retaining slide rails same as that shown in FIG. 8,which are connected to each other in a tee-connection by means of aconnector bar 53 same as that shown in FIG. 9 wherein a locking screw 54with a square washer 55 having the same construction as that shown inFIG. 11 frictionally locks up the boards 50, 51 and 52 to the connectorbar 53.

In FIG. 13 there is illustrated an end view of a locking plug 56 havinga square cross section at one extremity that includes a centrallydisposed threaded hole 57 with a countersink 58.

In FIG. 14 there is illustrated the full length of the locking plug 56that includes the other extremity opposite to one extremity having asquare cross section split into four prongs 59, 60, 61 and 62. Theinside dimension between two diametrically opposite prongs is tapereddown at the extremities of the prongs to a value slightly less than themaximum diameter of the threaded hole 57. When a flat countersunk headscrew is threaded into the threaded hole 57, the advancing shank of thescrew opens up the prongs 59, 60, 61 and 62 radially, and, consequently,they expand the noncircular hole of a square cross section included in aconnector bar such as element 8 of FIG. 2 or element 39 of FIG. 9resulting in a frictional locking between the retaining slide rails andthe retaining slide grooves.

In FIG. 15 there is illustrated the other end view of the locking plug56 where at it is split into four prongs 59, 60, 61 and 62. The lockingplug 56 may be used in conjunction with the connector bar 39 of FIG. 9or the connector bar 8 of FIG. 2 minus the countersink 16. The lockingscrew 17 shown in FIG. 5 and the locking screw 45 shown in FIG. 11 ismore preferable for the connector bars connecting reasonably thinboards, e.g., less than three quarters of an inch thick. The lockingplug 56 of FIG. 14 is preferred for connector bars connecting thickboards.

In FIG. 16 there is shown a front end view of a board 63 including aretaining slide rail 64 having a narrowed-down root 65 and asubstantially flat ridge 66 affixed to one extremity 67 of the board 63.

In FIG. 17 there is illustrated a front end view of a connector bar 68including four retaining slide grooves 69, 70, 71 and 72 disposed infour sides of the connector bar 68, respectively. Each of the retainingslide grooves has a cross section including a narrowed-down opening 73and a substantially flat bottom 74, that is matched to the cross sectionof the retaining slide rail 64 shown in FIG. 16. A noncircular hole 75with a square cross section is disposed coaxially through the length ofthe connector bar 68 wherein at least one extremity of the noncircularhole 75 includes a countersink 76. The noncircular hole is disposed insuch a way that the central portion of the cross section of theconnector bar 68 is substantially of a thin walled hollow square tubing.

In FIG. 18 there is illustrated a cross section of the connector bar 68taken along a plane 18--18 as shown in FIG. 17, wherein the noncircularhole 75 with a countersink 76 is further illustrated.

In FIG. 19 there is illustrated a front end view of two boards 77 and 78including retaining slide rails the same as that shown in FIG. 16, whichare connected to one another in an ell-connection by a connector bar 79having the same construction as that shown in FIG. 17. A locking screw80 the same as that shown in FIG. 5 threadedly engages the noncircularhole included in the connector bar 79 and frictionally locks up thesliding movement between the retaining slide rails and the retainingslide grooves. The unused retaining slide grooves are filled up by thefiller bars 81 and 82 slidably engaging the unused retaining slidegrooves and frictionally locked in position by the deformation createdby the locking screw 80.

In FIG. 20 there is illustrated a cross section of a filler bar 81 thatfills up an unused retaining slide groove flush to the side of theconnector bar. The filler bar 81 has the same cross section as theretaining slide rail 64 shown in FIG. 16 minus the base channel.

In FIG. 21 there is illustrated a front end view of a board 83 includinga dove-tail shaped retaining slide rail 84 affixed to one extremitythereof.

In FIG. 22 there is illustrated an end view of a connector bar 85including four dove tail shaped retaining slide grooves 86, 87, 88 and89 disposed in four sides of the connector bar 85, respectively. Thecross section of the dove-tail shaped retaining slide groove is matchedto the dove-tail shaped retaining slide rail 84 shown in FIG. 21. Theconnector bar 85 includes a noncircular hole 90 with a square crosssection coaxially disposed through the length of the connector bar 85wherein it is disposed in such a way that the central portion of thecross section of the connector bar 85 resembles a thin walled hollowsquare tubing. The noncircular hole 90 of the connector bar 85 may beengaged by the locking screw 45 shown in FIG. 11 or the locking plug 56shown in FIG. 14 that frictionally locks up the sliding movement betweenthe retaining slide rails and the retaining slide grooves by causing asmall deformation of the cross section of the connector bar. It shouldbe understood that the noncircular hole included in the connector barssuch as that shown in FIGS. 22, 17, 9 or 8 may be of a finite depthinstead of a through hole. It is not difficult to imagine that therewill be many variations in the combination comprising the crosssectional geometry of the retaining slide grooves and that of thenoncircular hole included in a connector bar that provides a frictionallocking by means of a small deformation in the cross sectionaldimensions of the connector bar created by a locking screw or lockingplug forcibly engaging the noncircular hole included in the connectorbar, which combinations differ in dimensions and geometry from theillustrative embodiments shown herein and, yet, rely on the sameprinciple as those of the present invention.

While the principles of the present invention have now been made clearby the illustrative embodiments, it will be immediately obvious to thoseskilled in the art many modifications of the arrangements, elements,proportion, structures and materials, which are particularly adapted tothe specific working environment and operating condition in the practiceof the invention without departing from those principles.

I claim:
 1. An universal slide connector with frictional locking meanscomprising in combination:(a) a slide connector bar having asubstantially square cross section including four sets of retainingslide grooves respectively disposed on four sides of said slideconnector bar in lengthwise direction, each of said four sets ofretaining slide grooves having a cross section comprising a convergingopening open to one side of said slide connector bar and a divergingextremity disposed adjacent to the geometrical center of the crosssection of said slide connector bar; and at least one noncircular holehaving a noncircular cross section disposed through the geometricalcenter of the cross section of said slide connector bar at at least oneextremity of said slide connector bar wherein said diverging extremitiesof said retaining slide grooves and said noncircular hole are separatedfrom each other by a thin section of material constituting said slideconnector bar; (b) a plurality of sets of retaining slide railsrespectively affixed to the extremities of a plurality of boards in aparallel relationship with respect to edges of said extremities of saidboards each of said plurality of sets of retaining slide rails having across section with a converging root and diverging extremities having acorresponding cross-section to the cross-section of said sets ofretaining slide grooves; and (c) a locking means engaging said at leastone noncircular hole disposed at at least one extremity of said slideconnector bar in an interfering relationship therebetween and deflectingsaid thin section of material intermediate said diverging extremities ofsaid retaining slide grooves and said noncircular hole;wherein saidplurality of retaining slide rails respectively affixed to theextremities of said plurality of boards slidably engaging at least twoof said four sets of said retaining slide grooves in said slideconnector bar and frictionally locked to each other by said lockingmeans deflecting said thin section of material adjacent to saidretaining slide grooves against said diverging extremities of saidretaining slide rails provide an ell, tee or cross-connection of saidplurality of boards.
 2. The combination as set forth in claim 1 whereinsaid at least one noncircular hole includes a circular countersinkdisposed coaxially to said noncircular hole at an extremity of saidslide connector bar, and said locking means comprises a countersunk headscrew with the maximum thread diameter slightly greater than the minimumdiagonal internal dimensions of said noncircular hole.
 3. Thecombination as set forth in claim 1 wherein said locking means comprisesan expandable plug having a cross section at one extremity substantiallymatched to the cross section of said noncircular hole.
 4. An universalslide connector with frictional locking means comprising incombination:(a) a slide connector bar having a substantially squarecross section including four sets of retaining slide groovesrespectively disposed on four sides of said slide connector bar inlengthwise direction, each of said four sets of retaining slide groovescomprising in combination a pair of elongated grooves disposed in askewed relationship to one another on a side of said slide connector barin a lengthwise direction wherein the cross section of the combinationof said pair of elongated grooves includes a pair of cut-outs ofsubstantially constant width and finite depth extending from said sideof said slide connector bar in a diverging configuration and at leastone noncircular hole having a noncircular cross section disposed throughthe geometrical center of the cross section of said slide connector barat at least one extremity of said slide connector bar wherein each ofsaid retaining slide grooves and said noncircular hole are separatedfrom each other by a thin section of material constituting said slideconnector bar; (b) a plurality of sets of retaining slide railsrespectively affixed to the extremities of a plurality of boards in aparallel relationship with respect to edges of said extremities of saidboards, each of said plurality of sets of retaining slide railscomprising in combination a pair of elongated rails disposed in a skewedrelationship to one another and extending from the extremities of saidboards wherein the cross section of said pair of elongated railsincludes a pair of extensions of substantially constant width and finiteheight extending from said extremities of said boards in a divergingconfiguration corresponding to the cross section of said sets ofretaining slide grooves; and (c) a locking means engaging said at leastone noncircular hole disposed at at least one extremity of said slideconnector bar in an interfering relationship therebetween and deflectingsaid thin section of material intermediate said retaining slide groovesand said noncircular hole;wherein said plurality of retaining sliderails respectively affixed to the extremities of said plurality ofboards slidably engaging at least two of said four sets of saidretaining slide grooves included in said slide connector bar andfrictionally locked to each other by said locking means deflecting saidthin section of material adjacent to said retaining slide groovesagainst said ridges of said retaining slide rails provide an ell, tee orcross connection of said plurality of boards.
 5. The combination as setforth in claim 4 wherein said at least one noncircular hole includes acircular countersink disposed coaxially to said noncircular hole at anextremity of said slide connector bar, and said locking means comprisesa countersunk head screw with the maximum thread diameter slightlygreater than the minimum diagonal dimensions of said noncircular hole.6. The combination as set forth in claim 4 wherein said locking meanscomprises an expandable plug having a cross section at one extremitysubstantially matched to the cross section of said noncircular hole. 7.An universal slide connector with frictional locking means comprising incombination:(a) a slide connector bar having a substantially squarecross section including four sets of retaining slide groovesrespectively disposed on four sides of said slide connector bar inlengthwise direction, each of said four sets of retaining slide grooveshaving a cross section comprising a narrowed-down opening open to oneside of said slide connector bar and a substantially convex bottomdisposed adjacent to the geometrical center of the cross section of saidslide connector bar; and at least one noncircular hole having anoncircular cross section disposed through the geometrical center of thecross section of said slide connector bar at at least one extremity ofsaid slide connector bar wherein said substantially convex bottoms ofsaid retaining slide grooves and said noncircular hole are separatedfrom each other by a thin section of material constituting said slideconnector bar; (b) a plurality of sets of retaining slide railsrespectively affixed to the extremities of a plurality of boards in aparallel relatonship with respect to edges of said extremities of saidboards each of said plurality of the sets of retaining slide railshaving a cross section with a narrowed-down root and a substantiallycorresponding concave ridge to the cross section of said sets ofretaining slide grooves, and (c) a locking means engaging said at leastone noncircular hole disposed at at least one extremity of said slideconnector bar in an interfering relationship therebetween and deflectingsaid thin section of material intermediate said convex bottoms of saidretaining slide grooves and said noncircular hole; wherein saidplurality of retaining slide rails respectively affixed to theextremities of said plurality of boards slidably engaging at least twoof said four sets of said retaining slide grooves included in said slideconnector bar and frictionally locked to each other by said lockingmeans deflecting said substantially convex bottoms of said retainingslide grooves against said substantially concave ridges of saidretaining slide rails provide an ell, tee or cross-connection of saidplurality of boards.
 8. The combination as set forth in claim 7 whereinsaid at least one noncircular hole includes a circular countersinkdisposed coaxially to said noncircular hole at an extremity of saidslide connector bar, and said locking means comprises a countersunk headscrew with the maximum thread diameter slightly greater than the minimumdiagonal dimensions of said noncircular hole.
 9. The combination as setforth in claim 7 wherein said locking means comprises an expandable plughaving a cross section at one extremity substantially matched to thecross section of said noncircular hole.
 10. An universal slide connectorwith frictional locking means comprising in combination:(a) a slideconnector bar having a substantially square cross section including foursets of retaining slide grooves respectively disposed on four sides ofsaid slide connector bar in lengthwise direction, each of said four setsof retaining slide grooves having a cross section comprising anarrowed-down opening open to one side of said slide connector bar and asubstantially flat bottom disposed adjacent to the geometrical center ofthe cross section of said slide connector bar; and at least onenoncircular hole having a noncircular cross section disposed through thegeometrical center of the cross section of said slide connector bar atat least one extremity of said slide connector bar wherein saidsubstantially flat bottoms of said retaining slide grooves and saidnoncircular hole are separated from each other by a thin section ofmaterial constituting said slide connector; (b) a plurality of retainingslide rails respectively affixed to the extremities of a plurality ofboards in a parallel relationship, each of said plurality of theretaining slide rails having a cross section with a narrowed-down rootand a substantially flat ridge corresponding to the cross section ofsaid retaining slide groove; and (c) a locking means engaging said atleast one noncircular hole disposed at at least one extremity of saidslide connector bar in an interfering relationship therebetween anddeflecting said thin section of material intermediate said substantiallyflat bottoms of said retaining slide grooves and said noncircularhole;wherein said plurality of retaining slide rails respectivelyaffixed to the extremities of said plurality of boards slidably engagingat least two of said four sets of said retaining slide grooves includedin said slide connector bar and frictionally locked to each other bysaid locking means deflecting said substantially flat bottoms of saidretaining slide grooves against said substantially flat ridges of saidretaining slide rails provide an ell, tee or cross-connection of saidplurality of boards.
 11. The combination as set forth in claim 10wherein said at least one noncircular hole includes a circularcountersink disposed coaxially to said noncircular hole at an extremityof said slide connector bar, and said locking means comprises acountersunk head screw with the maximum thread diameter slightly greaterthan the minimum diagonal dimensions of said noncircular hole.
 12. Thecombination as set forth in claim 10 wherein said locking meanscomprises an expandable plug having a cross section at one extremitysubstantially matched to the cross section of said noncircular hole.